package org.apache.lucene.util.fst;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.DataOutput;
import org.apache.lucene.util.IntsRef;

/**
 * Output is a sequence of ints, for each input term.
 *
 * @lucene.experimental
 */

public final class IntSequenceOutputs extends Outputs<IntsRef> {

    private final static IntsRef NO_OUTPUT = new IntsRef();

    private IntSequenceOutputs() {
    }

    public static IntSequenceOutputs getSingleton() {
        return new IntSequenceOutputs();
    }

    @Override
    public IntsRef common(IntsRef output1, IntsRef output2) {
        assert output1 != null;
        assert output2 != null;

        int pos1 = output1.offset;
        int pos2 = output2.offset;
        int stopAt1 = pos1 + Math.min(output1.length, output2.length);
        while (pos1 < stopAt1) {
            if (output1.ints[pos1] != output2.ints[pos2]) {
                break;
            }
            pos1++;
            pos2++;
        }

        if (pos1 == output1.offset) {
            // no common prefix
            return NO_OUTPUT;
        } else if (pos1 == output1.offset + output1.length) {
            // output1 is a prefix of output2
            return output1;
        } else if (pos2 == output2.offset + output2.length) {
            // output2 is a prefix of output1
            return output2;
        } else {
            return new IntsRef(output1.ints, output1.offset, pos1 - output1.offset);
        }
    }

    @Override
    public IntsRef subtract(IntsRef output, IntsRef inc) {
        assert output != null;
        assert inc != null;
        if (inc == NO_OUTPUT) {
            // no prefix removed
            return output;
        } else if (inc.length == output.length) {
            // entire output removed
            return NO_OUTPUT;
        } else {
            assert inc.length < output.length : "inc.length=" + inc.length + " vs output.length=" + output.length;
            assert inc.length > 0;
            return new IntsRef(output.ints, output.offset + inc.length, output.length - inc.length);
        }
    }

    @Override
    public IntsRef add(IntsRef prefix, IntsRef output) {
        assert prefix != null;
        assert output != null;
        if (prefix == NO_OUTPUT) {
            return output;
        } else if (output == NO_OUTPUT) {
            return prefix;
        } else {
            assert prefix.length > 0;
            assert output.length > 0;
            IntsRef result = new IntsRef(prefix.length + output.length);
            System.arraycopy(prefix.ints, prefix.offset, result.ints, 0, prefix.length);
            System.arraycopy(output.ints, output.offset, result.ints, prefix.length, output.length);
            result.length = prefix.length + output.length;
            return result;
        }
    }

    @Override
    public void write(IntsRef prefix, DataOutput out) throws IOException {
        assert prefix != null;
        out.writeVInt(prefix.length);
        for (int idx = 0; idx < prefix.length; idx++) {
            out.writeVInt(prefix.ints[prefix.offset + idx]);
        }
    }

    @Override
    public IntsRef read(DataInput in) throws IOException {
        final int len = in.readVInt();
        if (len == 0) {
            return NO_OUTPUT;
        } else {
            final IntsRef output = new IntsRef(len);
            for (int idx = 0; idx < len; idx++) {
                output.ints[idx] = in.readVInt();
            }
            output.length = len;
            return output;
        }
    }

    @Override
    public IntsRef getNoOutput() {
        return NO_OUTPUT;
    }

    @Override
    public String outputToString(IntsRef output) {
        return output.toString();
    }
}
